Conductor exploring coil



Get. 17, 1939. s, w, BQRDEN 2,176,756

CONDUCTOR EXPLORING COIL Filed April 2, 1938 2 Sheets-Sheet l 1 x-ucnfonOct. 17, 1939. w, B D 2,176,756

CONDUCTOR EXPLORING CO IL Filed April 2, 1938 2 Sheets-Sheet 2 Fig. 4-\/00 Patented Oct. 17, 1939 .UNETED STATES PATENr orrics CONDUCTOREXPLORING com Stephen W. Borden, Summit, N. J. Application April 2.192a, Serial No, 199,627

1 Claim.

My invention relates to apparatus for detecting the presence of a tracercurrent in an electri cal conductor By the term tracer current, I referto a current sent through a conductor either for the purpose ofassisting in identifying the conductor when it is one of a group ofseveral similar conductors or for the purpose of locating a fault in theinsulation of the conductor, the circuit being so arranged that thetracer current leaves the conductor at the fault.

Various types of tracer currents have been used, ranging from straightdirect current to high-frequency alternating current and includ-' ingpulsating currents, but as far as I am aware 15 a swing current has notpreviously been employed for this purpose. A detailed definition anddescription of swing current and swing current meters and their use fortesting will be found in myco-pending application, Serial No. 199,625.

One of the objects of my invention is to provide a pickup coil having anadjustable iron core which may be conformed, more or less, to the sizeand shape of a conductor enclosure and means of sensitizing the core toincrease the efficiency of the pickup coil and also the combination ofone or more of these elements with a swing current meter for detectingthe presence of swing current in a conductor. I In the drawings, Fig. 1is more or less schematic and shows the various devices employed and themanner in which they are connected up for locating a fault. Figs. 2 to 5inclusive are details of the flexible iron core and pickup coil.

Referring to the drawings (Fig. 1) binding posts 8 and 9 represent anysuitable source of swing current. Several types of swing currentgenerators are described in my co-pending applications, Serial Nos.199,625,,199,626, 199,630 and 199,632.

21 is an insulated electrical conductor inclosed in a lead sheath 34 andhoused in a fiber conduit 35. 28 is a fault which permits current toflow from conductor 21 to ground either directly or 45 via 24 and thelead sheath 34. 4B is an adjustable iron core on which is mounted a coil4|, the

terminal leads of which are connected to binding posts 58. 44 is a swingmeter and 45 a choke coil in series with the meter. A high resistance 50volume control 45A is shunted across the meter terminals.

I40 is a sensitizing device consisting of a transformer I32 having ahigh voltage secondary I33 which, with a condenser I3I in series, isshunted 5 across coil 4|; and aprimary winding A35 which may besupplied, via switch I34, with current from a battery, as E36, via aninterruptor I3! operated by winding I38. However, winding I35 may besupplied with (SO-cycle current in place of the interrupted batterycurrent. 20 and '2I are terminal binding posts to protect the meteragainst excessive voltage by shunting part of the current flow aroundthe meter when the voltage exceeds the flash point of the lamp.

The equipment within the dotted enclosure I40 is a unitary device havingtwo terminals and H for connection to an exterior circuit such as coil Mor some other source of swing current which it is desired to detect ormeasure.

50 is a transformer for supplying a low voltage w current at commercialfrequency and whose magnitude may be regulated by rheostat 5I. Oneterminal of the transformer secondary is connected, preferably viaresistance as 56, to a nondefective conductor, as 27, and the otherterminal connected to ground, as via water pipe I2I, the circuit beingcompleted via lead I22 which is connected to the other end of conductor2?.

In Fig. 2 the solid line diagram shows the flexible iron core 46adjusted to inclose a lead-covered conductor 32 which is of relativelysmall diameter, while the dotted diagram shows the core expanded toinclose a relatively large cable indicatedby the circle 35. In practice,the core may be required to encircle cables or their protective coveringranging from .25" to 6 in diameter. It will be understood, of course,that the iron core and pickup coil are more sensitive when the length ofthe magnetic circuit is relatively short, and it is therefore distinctlyadvantageous to be able to adjust the length of the magnetic circuit sothat the shortest feasible length may be employed for any particularsize of conductor or inclosing duct. Fig. 3 is a side elevation of thesolid line portion of Fig. 2.

Fig. 4 includes a plan view, on a larger scale, of a single laminationI00, and it will be seen that the entire flexible core is made up fromthis one form of lamination. Fig. 5 shows the method of assemblingthelaminations. I01 are tight-fitting rivets, positioned in openingsII3, by which the laminations are clamped securely together, while I I0is a loose-fitting rivet, positioned in openings II2, which permits thesections to swivel. However, since the laminations are se- 50 curelyfastened together by rivets I01 positioned on each side of the looserivet IIIl, the/laminations are necessarily pressed together quitesecurely in the swivel joints, thus providing a multiplicity of flat andfairly firm contact surfaces for carrying the flux from one section tothe next. In the center of each lamination is provided an opening H4 forthe reception of a clamping bolt, as I0i, for securing any two lectionstogether, for improving the'magnetic drcuit, as illustrated in Figs. 2and 3.

I prefer to make the core with a substant ally square cross-section, butthis is not essen 19.1. However, the sections should have flat surfaceson top and bottom which should be at least as wide'as the depth of thesection in order to provide a suitable flux path when two sections areclamped together, as in Figs. 2 and 3.

The equipment may be used in the following manner. The terminal 8 isconnected to conductor 21 via a lead 23 and a tracer current flowsthrough the conductor, thence through fault 28 andground circuit 29, 30,and SI, and thence via conductor 22 to terminal 9. When the conductor islead-incased and grounded to the lead, additional return circuits, as32, may be involved. The iron core 40 is now placed around the outsideof whatever enclosure may be provided for the conductor 21 and fastenedtogether by a bolt "H and nut I03 in such manner as to produce as shorta magnetic circuit asfeasible. The torminals 58 of the coil 4| are thenconnected, as by leads 42 and 43, to the posts 20 and 2| of the swingcurrent detector I50. The tracer current flowing in conductor 21produces a flux in core 40 which in turn generates a potential in coil4i which is registered on meter 44. Alternating current, of commercialfrequency, which may be flowing in lead sheath 34 or through any of theconductors which are surrounded by core 40, will produce a correspondingpotential in coil 4i, but the choke 45 prevents current of commercialfrequency flowing through meter 44 in any appreciable volume and suchcurrent as does flow will not register as meter 44 is nonresponsive tocurrents of commercial frequencies. If the potential exceeds volts lamp22 becomes conductive.

If we provide a GO-cycle current of approiiimately 10 amperes, as fromsource 50, and direct this ciu'rent through the ungrounded ca.- ble 21'and conductor I22 and return it to its source through any circuit whichis not inclosed by the core'40, such as water piping IZI, we are ineffect magnetizing core 40 with 10 ampere turns of GO-cycle current, andI have found that when this is done the sensitivity of coil 4i and meter44 in combination is increased about 5- i'old; by which I mean that if agiven tracer current will produce a deflection of one division on themeter without the sensitizing current,

then the swing will be increased to five divisions if this GO-cyclemagnetizing current is utilized.

In most cases, a more convenient method of sensitizing the core 40 is bymeans of a device, as I40, which has already been described and whichdevice will also increase a swing of one division to about fivedivisions. Of course, it is understood that the sensitizing current ofeither type has its maximum effectiveness when the tracer current itselfis at a minimum and of course is has no particular usefulness when thetracing current is of suflicient magnitude to give the desiredindications on the meter without its use.

As pointed out, alternating currents of commercial frequency, flowing ineither the lead sheath or one or more of the conductors, will have noappreciable effect upon the operation of the equipment, except toincrease its sensitivity, nor will steady flow direct current. Direct bythe use of the sensitizing equipment.

current flowing in the lead sheath which varies sharply from. time totime will produce potentials in coil 4! which in turn will be reflectedin meter 44, but this can only result in causing momentary interruptionsor variations in the swing of the needle which, of course, is constantlyswinging from one side to the other in step with the swing currentfrequency. Because of this immunity from interference by cormnercialcurrent, it is feasible to identify conductors by means of a swingcurrent tracer while they are alive and carrying full load. Lamp 22flashes over on abrupt and large changes in direct current.

If all or a part of the tracer current entering conductor 21 leaves byfault 28 and returns to terminal 9 by way of 34 and circuit 32, it willbe apparent that the efiective tracer current will be only thedifference between the current flowing in conductor 2! and that flowingin sheath 34. This is a difliculty which is present when any type ofinductive pickup device is used, and the usual practice of shunting someof the sheath current around the outside of the core 40 by means of aportable copper shunt applied to the cable sheath is equally applicableregardless of whether swing current or some other type of tracer currentis employed.

For purposes of demonstrating the utility of the equipment described, Iwill give a few ex amples of the sensitivity obtainable using a swingcurrent of 1.2 cycles per second and a swing current meter whichconsists of a permanent magnet-type direct current galvanometer having asensitivity of two microamperes per millimeter division and a potentialcircuit resistance of ohms. The choke coil 45 is rated at about 1100henrys and 6000 ohms D. C. resistance. The coil 4| may have a resistanceof about 6000 ohms and its current-carrying capacity need be only a fewmicroamperes. The core 40 may conveniently be made of laminations wideand built up to a thickness of about If the core be placed around aconductor about as shown in Fig. 2 and the conductor enclosure is about1" o. d., then, without using any sensitizing current either inconductor 21' or from the sensitizer I40, a current of 100 milliamperesflowing in conductor 21 will produce a swing of approximately onedivision on meter 44. If the core be expanded to encircle a conductorhousing of 6" o. d., then if the conductor carrying the tracer currentis located at approximately the center of the housing, a tracer currentof milliamperes will produce a deflection of one division on meter 44.Ineach case, this will be increased to between five and eight divisionsOnetenth division swing is easily detectable.

It has been demonstrated by careful tests that it is immaterial whetheror not the conductor is inclosed in an iron conduit or a steel armorjacket as these coverings have no more effect upon the readings than asimilar covering of fiber duct or other nonmagnetic material.

Of course, it will be understood that in actual practice the tracercurrent generator is located at the generating station or substation orother point at which the cable normally receives its current supplywhile the tracer pickup equipment is used anywhere along the length ofthe cable, usually in street manholes where the cables are rununderground, and thus is necessarily of a portable nature. The meter 44and choke coil 45 as well as the complete sensitizing 1| amass equipmentB are usually mounted in a suitable carrying case, as I50, and connectedto a pair of binding posts, as 20 and 2|, which in turn are connected tothe posts of pickup coil H by flexible leads, as 42 and 43, which may beof any desired length, permitting the meter to be used at the surface ofthe ground while the pickup coil is used in a manhole.

Since the detector is non-responsive to other than swing current, theconductor under test may be one of two or more conductors of a workingcircuit but in making such tests it is necessary that all the conductorsof the circuit pass through the pickup loop and the system must be freefrom grounds other than the fault.

While I have described certain features more or less in detail, it willbe understood that the invention will employ various devices ofdiffering forms and construction and it is to be understood that theinvention is not to be limited except by the scope of the appended claimtaken in conjunction with the state of the prior art.

I claim:

' Means for detecting swing current in a conductor, which includes aniron core forlencircling the conductor, a coil on the core, leadsconnecting the terminals of the coil with a swing meter. and asensitizing circuit connected to the terminals of the coil, whichcircuit includes the high voltage winding of a transformer the primarywinding of which is energized by a source of current having a frequencyof not less than 50 cycles per second. STEPHEN W. BORDEN.

